1. Technical Field
The present invention relates to a vehicle air conditioner suitable for electric cars, and more particularly to a vehicle air conditioner that reduces compressor noise during air conditioner transition from an on state to an off state.
2. Discussion
In an electrically-powered vehicle, an electric motor typically provides the driving force for a conventional air conditioner compressor. An air conditioning switch connected to the motor may be turned on immediately after it is turned off due to improper handling during the operation of the compressor. Because a difference between high and low pressures of the coolant remains in the refrigerating cycle immediately after the compressor is stopped, a greater driving force is required to restart the compressor than that required when the pressure in the refrigerating cycle is uniform.
In such a case, the compressor can not respond to an air conditioner operational request until the pressure difference in the refrigerating cycle reaches a restartable state, because the driving force of the electric motor is smaller than that supplied to a compressor from an internal combustion engine.
As a solution to this problem, Japanese Patent Application Laid-Open No. 62-37630 discloses an air conditioner which stops the operation of a refrigerating cycle by stopping a compressor after reducing the speed of rotation of the compressor gradually to achieve a uniform pressure of the coolant in the refrigerating cycle.
However, since a compressor is operated after an instruction to stop air conditioning is issued until the pressure of the coolant in the refrigerating cycle becomes uniform, the compressor tends to make unpleasant noises when the vehicle is at low speed or when the blower level is low.